NASA photographs mile-wide asteroid approaching Earth with its own moon

Asteroids contain the answers to the formulation of the solar system and the wider galaxy while also being potentially deadly depending on their size, which is why it's a great idea to keep an eye out for as many as we can - particularly the big ones.

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One such space beast was discovered in 2011 as it was making a close approach with Earth. The asteroid, now dubbed 2011 UL21, made its close approach to Earth only recently on June 27, and while it zoomed by, NASA researchers captured close-ups of it, revealing details that are scarcely seen during asteroid observation. 2011 UL21 is a mile-wide asteroid and when it passed Earth it was scanned by radar revealing a tiny moonlet orbiting the larger body.

This isn't the first time a large asteroid has been found having its own moon, as NASA calls these asteroids binary systems and even believes around two-thirds of asteroids as big as 2011 UL21 have their own moon. However, photographing them is another challenge entirely.

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Using the Goldston Solar System Radar, a 230-foot dish that earns its title of the world's largest fully steerable radar antenna, honed its instruments on the asteroid as it made its approach at a distance of 4.7 million mores, it was able to capture the above and below imagery. The small moonlet was found to orbit at a distance of 1.9 million miles.

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"There was no risk of either near-Earth object impacting our planet, but the radar observations taken during these two close approaches will provide valuable practice for planetary defense," the team noted.

"It is thought that about two-thirds of asteroids of this size are binary systems, and their discovery is particularly important because we can use measurements of their relative positions to estimate their mutual orbits, masses, and densities, which provide key information about how they may have formed," said Lance Benner, principal scientist at JPL